This invention relates to the control of a heater associated with the crankcase of a compressor. In particular, this invention relates to monitoring the status of such a crankcase heater.
Compressors are utilized in many modem heating, cooling, and refrigeration applications. These compressors require oil to lubricate the moving parts of the compressor. The oil is often housed in a crankcase where it can be drawn up into the moving parts of the compressor. Heaters have been previously provided to heat the crankcase oil so as to boil off liquid refrigerant in the oil and maintain an appropriate viscosity of the oil for lubricating the moving parts of the compressor. The crankcase heater may run continuously or it may be activated in response to sensed conditions either in the crankcase or in other areas of either the compressor or the system in which the compressor operates. An example of the latter type of control is disclosed in commonly assigned U.S. Pat. No. 5,012,652 entitled xe2x80x9cCrankcase Heater Control for Hermetic Refrigerant Compressorsxe2x80x9d issued to Kevin Dudley. The above described crankcase heater control as well as other heater controls all require one or more invasive sensors to sense conditions that are to be fed back to the control. These controls also do not necessarily provide a quick check as to whether a crankcase heater is operating properly shortly after it has been turned on since there is a lag between activation and changes to the sensed conditions fed back to the control.
It would be preferable to obtain information as to the operation of a crankcase heater without resorting to the use of invasive sensors. It would also be preferable to be able to quickly determine whether a crankcase heater is operating properly even if other systems may be deployed that use invasive sensors.
Briefly, the present invention senses the current flowing through a resistance heater. The resistance heater may be either located in the crankcase or external to the crankcase. The sensing is preferably accomplished by a transformer in combination with an amplifier providing a feedback signal to the programmed microprocessor. The transformer is installed in the line which carries the electrical current flowing through the resistance heater. The microprocessor checks for the presence of an appropriate voltage level from the amplifier. In the event that the voltage level is not above a threshold level, the microprocessor sends an alarm signal indicating that the crankcase heater is not operating properly.